As an illumination means for liquid crystal display panel, a sidelight type planar illumination apparatus (back light) in which a small light emitting diode (LED) with excellent environmental adaptability is arranged along an light-receiving end surface of a light guide plate has been widely employed mainly in the field of miniaturized portable information devices such as cell phones. In such a kind of the planar illumination apparatus, LED is generally mounted on a flexible printed circuit board (hereinafter, referred to as “FPC”) and arranged along the light-receiving end surface of a light guide plate. In recent years, in connection with a thickness reduction of an information apparatus, a further reduction in thickness of the planar illumination apparatus has been also strongly desired. In addition, the arrangement/configuration of FPC has been proposed in various ways depending on the demand (see, for example, Japanese published unexamined application Nos. 2009-216753 and 2007-128820).
FIG. 5 is a cross-sectional side view illustrating the main part of a planar illumination apparatus described in Japanese published unexamined application No. 2009-216753. The planar illumination apparatus 100 is used as a back light of a liquid crystal panel 120 and includes a light guide plate 116. On the output surface 116a side of the light guide plate 116, an optical compensation sheet 115 composed of a diffusion plate and a prism plate is disposed by lamination. On the back side 116b of the light guide plate 116, a reflective sheet 107 is disposed. In addition, a LED 112 mounted on a FPC 105 is arranged along the light-receiving end surface 116c of the light guide plate 116, and the FPC 105 itself is fixed on a mold frame 106 with a double-sided tape 111.
In the planar illumination apparatus 100, as shown in part A in the figure, the tip of the FPC 105 and the reflective sheet 107 are disposed facing each other (i.e., being faced to each other at a minute interval or butted each other to avoid an increase in thickness due to the lamination of FPC 105 and reflective sheet 107.
FIG. 6 is a cross-sectional side view of the main part of a planar illumination apparatus described in Japanese published unexamined application No. 2007-128820. The planar illumination apparatus 200 is used as a back light of a liquid crystal panel 220 and includes a light guide plate 216. On the output surface 216a side of the light guide plate 216, an optical sheet 215 is disposed by lamination. On the back surface 216b side of the light guide plate 216, a reflective sheet 207 is disposed. A LED 212 mounted on a FPC 205 is arranged along the light-receiving end surface 216c of the light guide plate 216, and the light-receiving end surface 216c side of the light guide plate 216 is housed in a back case 206 together with the LED 212.
In the planar illumination apparatus 200, a thin portion 207a is formed in a reflective sheet 207 and the FPC 205 is then disposed by lamination on the thin portion 207a to avoid an increase in thickness.